The regulation of RNA synthesis during growth transitions from non-proliferating to the proliferating state represents the major thrust of this research. New information on the changing patterns of RNA synthesis and the mechanism(s) involved in the regulation of these RNA syntheses during hormone-induced tissue proliferation should result from these studies. Sequence complexity studies and in vitro translation of total and poly(A) RNA, including ribosome-associated mRNA, will be assessed as another approach to evaluate the possible role of changing patterns of RNA synthesis in the onset and/or cessation of tissue proliferation. Changes in the abundant class poly(A) RNAs will be assessed in detail, making use of recombinant-cDNA technology coupled with in vitro translation studies of the poly(A) RNA. The mechanism(s) by which RNA polymerase I activity is rapidly modulated during growth transitions will be assessed. The enhanced synthesis of rRNA, and the resultant ribosome formation, is one of the earliest events associated with the induction of tissue proliferation (e.g. neoplasia, liver regeneration, PHA-, serum- and hormone-induced causal relationship 1) between the regulation of ribosome synthesis and function and 2) between these changes and the onset of tissue proliferation.